United States Patent im
Takahashi et al.
[li] Patent Number: [45] Date of Patent:
[54] FLUORESCENT COMPOSITION
[75] Inventors: Fumio Takahashi, Odawara;
Kunihiko Yoneshima, Hiratsuka;
Takashi Hase, Ebina, all of Japan
[73] Assignee: Kasei Optonix, Ltd., Tokyo, Japan
[21] Appl. No.: 259,526
[22] Filed: Oct. 18,1988
[30] Foreign Application Priority Data
Oct. 19, 1987 [JP] Japan 62-263224
[51] Int. CI.' C09K 11/54; F21V 9/00
[52] U.S. Q 252/301.60 S; 252/301.6 R;
252/301.4 S; 252/582 [58] Field of Search 252/582, 301.6 R, 301.6 S,
252/301.4 R, 301.4 S
[56] References Cited
U.S. PATENT DOCUMENTS
4,106,946 8/1978 Ritze 252/582
FOREIGN PATENT DOCUMENTS
2747509 4/1979 Fed. Rep. of Germany ... 252/301.6 S 63-284290 11/1988 Japan 252/301.5 S
Primary Examiner—John S. Maples
Assistant Examiner—Philip Tucker
Attorney, Agent, or Firm—Obion, Spivak, McClelland,
Maier & Neustadt
[57] ABSTRACT
A fluorescent composition composed of a mixture of a sulfide phosphor and a conductive material, the sulfide phosphor consisting essentially of a sulfide of the formula (Zni_x, Cd;t)S wherein x is a number satisfying a condition of O^xSl, as host material, and zinc oxide (ZnO) or a compound capable of being converted to zinc oxide (ZnO) by heat treatment and alumina, adhered to the surface of the host material.
4 Claims, 2 Drawing Sheets
'1 1 1 1 I i l t L_
200 400 600 800 1000
AMOUNT OF ADHERED ALUMINA (ppm)
U.S. Patent July u, 1991 sheet 2 of 2 5,032,316
FLUORESCENT COMPOSITION
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improvement of a fluorescent composition. More particularly, it relates to a fluorescent composition capable of emitting light of high luminance under low-velocity electron excitation at an acceleration voltage of not higher than a few hundreds volts and having the decrease in luminance with time during the use for a long time reduced.
2. Description of Background
Zinc activated zinc oxide phosphors (ZnO:Zn) are well known as phosphors which can emit light of high luminance under excitation by low-velocity electron beams at an acceleration voltage of not higher than 1 kV, particularly not higher than a few hundreds volts. When excited by low-velocity electron beams, the ZnO:Zn phosphors emit green-white light of high luminance, and the fluorescent display devices having fluorescent screens composed of such ZnO:Zn phosphors are widely used as display elements for table-top calculators, various meters for vehicles and electrical appliances such as VTR.
In recent years, reflecting the expansion of the field of the application of the fluorescent display devices, a variety of emitting colors are desired for the fluorescent display devices. Various developments have been made on the fluorescent materials which are capable of emitting light other than green light under low-velocity electron excitation. As a result, some fluorescent materials have been developed. Among them, fluorescent compositions are known which are prepared by mixing a conductive material such as indium oxide ... zinc oxide (ZnO) or tin oxide (SnOj) to a sulfide phosphor consisting essentially of a sulfide of the formula (Zni-*, Cdx)S wherein x is a number satisfying a condition of 0Slx=l, as host material, which is activated by zinc (Zn), silver (Ag), gold (Au), copper (Cu) or manganese (Mn) and, if necessary, co-activated by halogen, aluminum (Al), gallium (Ga) or indium (In) (Japanese Examined Patent Publications No. 33153/1984 and No. 33155/1984 and Japanese Examined Patent Publication Nos. 44035/1987 and 53554/1987). (A phosphor consisting essentially of a sulfide of the formula (Zni_x, Cd^)S wherein x is a number satisfying a condition of 0Six5=1, as host material, will generally be referred to hereinafter as "a (Zni_^, Cd^)S type sulfide phosphor".) When excited by low-velocity electron beams at an acceleration voltage of not higher than 1 kV, these fluorescent compositions exhibit emission of visible lights of high luminance ranging from blue to red depending upon the solid solution ratio (x value) of Cadmium (Cd) to Zinc (Zn) in the (Zni-*, Cdx)S type sulfide phosphor host material as one of the constituting components of the fluorescent compositions or upon the combination of activators and co-activators. Therefore, by using such fluorescent compositions as fluorescent screens, it has been made possible to obtain a variety of 60 colors for fluorescent display devices, and the amount of information has been remarkably improved. However, fluorescent display devices using, as fluorescent screens, fluorescent compositions composed mainly of such (Zni_^, Cd^)S type sulfide phosphors, have a serious drawback that when operated for a long period of time, there will likely be a decrease in luminance of the fluorescent layer or non-uniformity in emission,
which is considered to be attributable to a deterioration of the (Zni-*, Cdx)S type sulfide phosphor in the fluorescent screen, or deposition of a decomposed product of the phosphor to the filament. Therefore, it has been desired to develop a fluorescent composition which hardly undergoes a deterioration or decomposition even under excitation by low-velocity electron beams for a long period of time and which scarcely brings about a decrease in luminance or non-uniformity in
The present invention has been made in view of such a desire. It is an object of the present invention to provide a fluorescent composition which exhibits emission of light of high luminance under excitation by lowvelocity electron beams and which is less susceptible to deterioration or decomposition when used as a fluorescent screen for emission of light for a long period of time and which scarcely brings about a decrease in luminance with time or non-uniformity of emission of the fluorescent layer.
The present inventors have conducted various studies on the surface treatment of the (Zni_x, Cd^)S type sulfide phosphors, particularly the surface treating agents, in order to accomplish the above object. As a result, it has been found possible to accomplish the above object by using a (Zni_x, Cd^S type sulfide phosphor treated for adhering zinc oxide (ZnO) or a compound capable of being converted to zinc oxide (ZnO) by heat treatment (hereinafter referred to generally as a Zn compound) and alumina simultaneously on the surface of the (Zni_x, Cdx)S type phosphor, as a constituting component of the fluorescent composition. The present invention has been accomplished on the basis of this discovery.
The present invention provides a fluorescent composition composed of a mixture of a sulfide phosphor and a conductive material, the sulfide phosphor consisting essentially of a sulfide of the formula (Zni_jr, Cd^S wherein x is a number satisfying a condition of 0=xSI 1, as host material, and zinc oxide (ZnO) or a compound capable of being converted to zinc oxide (ZnO) by heat treatment and alumina, adhered to the surface of the host material.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph showing the relation between the amount of alumina adhered to the sulfide phosphor contained in the fluorescent composition and the initial luminance of the fluorescent display device using this fluorescent composition.
FIG. 2 is a graph showing the relation between the amount of alumina adhered to the sulfide phosphor contained in the fluorescent composition of the present invention and the luminance after the operation for 1,000 hours of the fluorescent display device using this fluorescent composition.
DETAILED DESCRIPTION OF THE
PREFERRED EMBODIMENTS
Now, a method for the preparation of the fluorescent composition of the present invention will be described.
The method for the preparation of the fluorescent composition of the present invention is the same for the preparation of the conventional fluorescent composition composed of a mixture of a phosphor and a conduc
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